Question

我正在寻找async / await中的一些最佳实践。我有datepicker和observable集合，我想在异步更改的datetime上将数据加载到observable集合中。我怎样才能修改我的代码来做到这一点，很好？我知道，属性不能是异步的。我知道命令，所以也许我需要在datepicker datetimechanged事件上绑定async命令？

public class LogViewModel : ViewModelBase
{
    public LogViewModel()
    {
        LogCollection = new ObservableCollection<Log>();
        DateTime = DateTime.Now.Date;
    }

    private DateTime _dateTime;

    public DateTime DateTime
    {
        get { return _dateTime; }
        set
        {
            if (_dateTime != value)
            {
                _dateTime = value;
                LogCollection.Clear();

                //long running code begins
                using (var ctx = new DataContext())
                {
                    ctx.Logs.Where(p => p.dt >= _dateTime && p.dt < _dateTime.AddDays(1))
                        .ToList().ForEach(z => LogCollection.Add(z));
                }
                RaisePropertyChanged("DateTime");
            }
        }
    }

    public ObservableCollection<Log> LogCollection { get; set; }
}

Answer 1

我认为最佳做法是保持VM和类似的类清晰。所以我更喜欢在内部订阅PropertyChanged事件并将这样的逻辑移动到事件处理程序（重构友好示例）：

public LogViewModel()
{
    if (!DesignerProperties.IsInDesignTool)
    {
        PropertyChanged += HandlePropertyChanged;
    }   
}       

private static string DateTimePropertyName = ExpressionHelper.NameOf((LogViewModel _) => _.DateTime);

private void HandlePropertyChanged(object sender, PropertyChangedEventArgs e)
{
    if (e.PropertyName == DateTimePropertyName)
    {
        //Start async operation in other thread via TPL Tasks/ThreadPool's QueueUserWorkItem etc. for example or using true-async IO operations (a bunch of real-async operations available in EF)
    }
}

Async / await On Property Changed

1 个答案: